NEWS & PRESS

Scientists could soon be able to observe the shockwaves between the magnetic fields of planets and the flow of charged particles from the stars they orbit, according to an astronomer at the University of St Andrews. The fields (magnetospheres) shield the atmospheres of planets and are thought to be crucial to the development of life. Now PhD student Joe Llama has worked out how the shock waves affect the dip in light seen from Earth as the planet passes in front of its parent star. He will present the new model on 5 July at the National Astronomy Meeting in St Andrews, Scotland.

illustration of how material ejected from the Sun (on the left) interacts with the magnetic field of the Earth (on the right). The white lines represent the solar wind; the purple line is the bow shock line and the blue lines surrounding the Earth represent its protective magnetosphere. Credit: NASA. Click for a larger imageSince the early 1990s astronomers and space scientists have found almost 900 planets in orbit around other stars, most of which are far larger than the Earth and far closer to their stars than the Earth is to the Sun. These giant planets are known as ‘hot Jupiters’ because of their sizes and high atmospheric temperatures, in some cases several thousand degrees.

Hot Jupiters have magnetospheres that help protect them to some extent from the high-energy particles that flow from their stars (so-called stellar winds). When the wind hits the planetary magnetospheres they interact in a ‘bow shock’ that diverts the wind and compresses the magnetic field.

Joe Llama looked at earlier work on the planet orbiting the orange dwarf star HD 189733, located 63 light years away in the direction of the stars of the constellation Vulpecula. From Earth the planet, HD 189733b, blocks the light of the star every two days, an event known as a transit, causing a dip in its brightness. Measuring the way the light drops over time gives scientists a lot of information on the planet and star, including their sizes and the makeup of their atmospheres.

As a relatively bright star, HD189733 has been studied extensively by astronomers. Magnetic imaging of the star has revealed that the star has a magnetic field approximately thirty times stronger than that of our Sun. The presence of such a strong magnetic field means that the stellar wind is likely to be much more powerful than the Solar wind. The scientists at the University of St Andrews have also carried out simulations of the stellar wind around HD189733 using the magnetic maps to examine how dangerous this wind is likely to be for the planet.

Looking at the predicted transits in more detail, Joe and his colleagues have found that the shockwave between the stellar and planetary magnetic fields will change drastically as activity on the star varies. As the planet passes through very dense regions of the stellar wind, so the shock will become denser, the material in it will block more light and therefore cause a larger dip in the transit making it more detectable.

An artist’s impression of the hot Jupiter planet in orbit around the star HD 189733. Credit: ESA – C. Carreau. Click for a larger imageTheir simulations show that the conditions the planet sees as it orbits around its star are going to change dramatically during a single orbit around the star. They find that the magnetosphere, which protects the planet from the radiation of the stellar wind, will experience huge changes in size and orientation which could have devastating consequences for the atmosphere of the planet.

In the case of HD 189733b, this is not a huge problem as it and other hot Jupiters are already far too hostile for life to survive. But strong stellar winds could also strip away the atmospheres of potentially habitable planets further out, something that would have dire consequences for their habitability. Joe comments: “Imagine what the Earth would be like with its air stripped away, placed in a radiation bath. There could be numerous planets like this that in many ways resemble our world, but where life never stood a chance.”

If astronomers look at the way in which the light curves of transits change, they should be able to observe the varying stellar winds and their effects, helping to better identify potentially habitable worlds. Joe concludes: “For more than two decades we have been stepping up the search for other planets like the Earth. Our new work will help refine this quest, enabling us to rule out the sites where dangerous activity on stars would kill off life from the start.”

http://star-www.st-andrews.ac.uk/~jl386/shocks Joe Llama’s page on this work. The top section of the movie shows the planet and its associated magnetosphere bow shock moving in front of its host star. In the bottom half is a representation of how this affects the light from the system observed on Earth. The solid line shows the dimming due to the planet and bow shock combined and the dashed line the dimming due to the planet alone. Credit: Joe Llama

Notes for editors

Bringing together more than 600 astronomers and space scientists, the RAS National Astronomy Meeting (NAM 2013) will take place from 1-5 July 2013 at the University of St Andrews, Scotland. The conference is held in conjunction with the UK Solar Physics (UKSP: www.uksolphys.org) and Magnetosphere Ionosphere Solar Terrestrial (MIST: www.mist.ac.uk) meetings. NAM 2013 is principally sponsored by the RAS, STFC and the University of St Andrews and will form part of the ongoing programme to celebrate the University’s 600th anniversary.

Meeting arrangements and a full and up to date schedule of the scientific programme can be found on the official website at http://www.nam2013.co.uk

The Royal Astronomical Society (RAS: www.ras.org.uk, Twitter: @royalastrosoc), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organises scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3500 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

The Science and Technology Facilities Council (STFC: www.stfc.ac.uk, Twitter: @stfc_matters) is keeping the UK at the forefront of international science and tackling some of the most significant challenges facing society such as meeting our future energy needs, monitoring and understanding climate change, and global security. The Council has a broad science portfolio and works with the academic and industrial communities to share its expertise in materials science, space and ground-based astronomy technologies, laser science, microelectronics, wafer scale manufacturing, particle and nuclear physics, alternative energy production, radio communications and radar. It enables UK researchers to access leading international science facilities for example in the area of astronomy, the European Southern Observatory.

Founded in the 15th century, St Andrews is Scotland’s first university and the third oldest in the English speaking world. Teaching began in the community of St Andrews in 1410 and the University was formally constituted by the issue of Papal Bull in 1413. The University is now one of Europe’s most research intensive seats of learning – over a quarter of its turnover comes from research grants and contracts. It is one of the top rated universities in Europe for research, teaching quality and student satisfaction and is consistently ranked among the UK’s top five in leading independent league tables produced by The Times, The Guardian and the Sunday Times.

The University is currently celebrating its 600th anniversary and pursuing a £100 million fundraising campaign, launched by Patron and alumnus HRH Prince William Duke of Cambridge, including £4 million to fund the creation of an ‘Other Worlds’ Think Tank and Observatory. The new think tank and Observatory project will extend the University of St Andrews’ flagship work on extra-solar planets, and provide a creative environment for problem-focused research, education and continuing public engagement.